This chapter deals with the liver function, renal function and thyroid function tests. Liver plays a major role in the metabolism. There is no single test to detect the abnormality of the liver because of the variety of the functions performed by the liver. Therefore, there are group of tests available to detect the abnormality of the liver. Detection of total protein, albumin, AST, ALT, bilirubin and GGT helps in the diagnosis of liver diseases and to diagnose the jaundice. Kidneys perform many important functions to regulate the internal environment of the human body. It is the main regulator of all the subs­tances of body fluids and responsible for maintaining homeostasis. The major functions of the kidneys are Kidneys urine formation, regulation of fluid and electrolyte balance, regulation of acid-base balance, hormonal function, excretion of non-protein nitrogenous substances substances. The serum urea and creatinine determination helps to detect the abnormal function of the kidneys. Thyroid gland secretes T3 and T4 upon stimulation by TSH. The reduced level of thyroid hormones is called hypothyroidism (goitre, Hashimoto\'s thyroiditis). The high level of thyroid hormones (hyperthyroidism) seen in Graves\' disease, Thyroiditis and Toxic multi-nodular goiter. Thyroid Iodine Uptake Scan means of measuring thyroid function is to measure how much iodine is taken up by the thyroid gland.